Onboard guitar FX _ MBP Harmonic Energizer _ pot value ?

[isophase]

Hi there,
This is my first post on the forum. I Hope this is the correct section for asking my question.

I'm trying to install a Harmonic Energizer FX pedal onboard my stratocaster, and I'm not sure about pot value and if its a problem or not.

My strat is already equipped with 500Kohm push pull pot and i would like to re-use it for this project.
I would like to use the push pull pot to bypass the FX and also use the pot as the frequency sweep control when the effect is "on".
BUT the Harmonic Energizer calls for 50Kohm value for frequency sweep, and my push pull pot is 500Kohm. Is it a problem? how is 500Kohm instead of 50Kohm affect the range for controlling the frequency sweep?
or should i add 50Kohm resistor in paralelle with the pot to make the value "closer" to original value?

Thank you for your help and advice, and any good suggestions!
Best,
Jonathan

[Mark Hammer]

Unfortunately, not only the value of the guitar pot, compared to that on the HE circuit, is a problem, but so is the DPDT nature of the switch on the pot.  The 500k pot simply can not be co-opted for another function very easily.  I suspect the most practical solution is to use a 50k trimmer on the circuit board, use the pot switch to bring the HE in and out of circuit, and drill a small hole in the control plate to allow adjustment of the frequency trimmer.  I am assuming, perhaps naively, that the guitar has thru-body mounted pots, and a control cavity with a backplate.  If the quitar in question is a Strat-like instrument, then all bets are off.

[willienillie]

Are you talking about a traditional Strat with 3 knobs (1 vol, 2 tone)?  Since you mention 500k and push/pull, I guess not.  But if close to that setup, you can rewire to have only one master tone pot, and use the extra spot for your 50K sweep pot.  Then you should be able to use the DPDT as a true bypass for the effect, as long as you don't want that switch to do anything else.

[isophase]

At the moment (actually since more than 20 years now :-) my strat has x1 master volume and x1 master tone.
Tone control is the push pull pot and the switch splits the pickup bobins.
In place of the original second tone control, there is a toggle switch there to activate the bridge pickup when the selector is in the neck or center position, so that i can have all pickups active at the same time. I very seldom use this and can live without it.

My strat is at my luthier shop at the moment and is beeing converted to hardtail. i've been wanting to do this since many years since i never use the vibrato, and so I asked him to remove the vibrato system and fill in the hole with a wood block. Now i can use the space on the back to install the PCB and 9V battery in place of the vibrato springs.

I was thinking of removing the tone control alltogether and make it > x1 master volume, x1 push pull pot to activate the effect and control the center frequency, and remove the small toggle switch and add a third pot in place for controlling the bandwidth (Q) from the effect. 

Indeed, planning to use some small trimmer/pots for controling Gain and Output Volume with a screw driver from the back of the guitar (with a perforated backplate for access to the trimmer/pots).
These two controls, Gain and Output Volume are not critical in the sense they won't need much manipulation once "tuned in" and set correctly, so no problem if they're not directly accessible.
But frequency and B.W. control i find quite very useful to have "on hand" access.

The "sad" thing is, this way two knobs now occupy a lot of space but they're only usefull when the effect is active, so not very optimal in terms of "design ergonomics"

Also, i like the tone control of my strat and it would be nice if i can keep it. So mabe another way of doing this would be :
x1 master volume / x1 master tone (w/fx bypass switch) and x1 double stack pot (Q and freq. control).

I don't like double stack potentiometres so much as they're quite big and ugly :-) but lets see if i can find some nice small knobs that i like and mabe try this option.

Or mabe keep the guitar as is > Master Vol / Master Tone and drill just one hole and try to install two miniature pots?

Sometime i see some "miniature green pots" on some project photos, what is the brand and where to find?

mabe this will fit in my strat? lets see, mabe this is the good solution! x1 master Vol. / x1 master Tone (w/FX bypass switch) and two tiny pots for Q & Freq control, and this would solve problem make do with a "wrong" value potentiometer. 

all suggestion welcome
Thanks!

Jonathan

[Mark Hammer]

My own long-held view on on-board FX is that a guitar should probably only have those electronics that can not be accomplished easily, or at all, off the guitar, or those electronics that are accomplished more effectively on the guitar than on the floor (e.g., buffers).

If one has multiple guitars, on the other hand, and can treat a guitar with one or more on-board circuits as a specialized tool, to be selected for specific jobs, replaceable with other guitars when needed, then go for it.  But I think "main" guitars should be left as generic and sonically maleable as possible.

[isophase]

Hi there,

i finished the work on my strat, I'm soooooo happyyyyyyy !!!!!!
The onboard effect is working really good and really fun to play with!

So in the end this is what i did : i kept the original master volume and master tone, and drilled just one additionnal hole for the freq. sweep (+on/off switch) and bandwidth control. i place an 50Kohm resistor in parallel with the 500Kohm push pull pot to adapt it to the HE circuit.
Its working really good, only the range of the pot for the frequency sweep will need to be adjusted a bit. As it is now, its a bit too sensitive in the "low range" of the pot. Small rotation of the pot make a too wide frequency change in the low range. But its not so critical and i think its working really good as is. I will need to try with a linear pot, i can only find some 250Kohm linear push/pull pots, this with a 50Kohm in parallel i think it would work better than my actual 500Klog+50Kohm resistor in parallel... lets find out...

Some photos

   

[Mark Hammer]

Nice work.  You now have a Zappa-approved guitar! 

[isophase]

Thank you!
inspired by zappa indeed